The present invention relates to a loose tube cable having a binder which is easily removable when the cable is accessed. In particular, the present invention relates to a loose tube cable having ripcord disposed under a binder surrounding a plurality of buffer tubes for ripping a binder and an outer protective jacket. This invention also relates to a binder formed of a material which is weakened or melted by the application of heat when the loose tube cable is jacketed.
In conventional loose tube cables, buffer tubes are stranded (helically or reverse helically) around a central strength member to form a stranded core. The buffer tubes are utilized as the primary structure for protecting the thin optical fibers contained within. That is, the buffer tubes house an optical unit such one or more loose optical fibers or an optical fiber ribbon comprising a plurality of optical fibers which are held together in a planar array. The buffer tubes are generally filled with a water blocking component such as a thixotropic gel which prevents water ingress but allows for fiber movement during cable expansion or contraction, or contain a water swellable material which absorbs water. In addition to the buffer tubes, filler rods may be stranded around the central strength member in order to provide symmetry in design for fiber counts lower than that of a full fiber count cable.
After the buffer tubes (and filler rods) are stranded around the central strength member, one or more binders are wrapped around the buffer tubes in order to hold the buffer tubes in place prior to extrusion of a cable jacketing material about the stranded core. The binders are typically tape-like members or filaments made of polyester and aramide materials and may be helically or contra-helically applied. Next, the stranded core which is held together by the binder is wound on a reel at the end of the stranding line and moved to a jacket line where one or more ripcords (typically two ripcords which are 180 degrees apart) are disposed over the stranded core and a plastic material, e.g., polyvinyl chloride (PVC), polyethelene, polypropolyene, or copolymer thereof, is extruded to form a protective outer jacket around the ripcord and stranded core. Once the cable has been jacketed, the binders surrounding the buffer tubes are no longer necessary because the jacket now serves hold the loose tubes in place.
The ripcords disposed between the outer jacket and the stranded core are provided for ripping the outer jacket in order to access the buffer tubes in the loose tube cable. That is, when it is necessary to access the optical fibers in the loose tube cable, e.g., prepare the optical fibers for splicing, the ripcord is pulled with sufficient force to rip the outer jacket and the binders are removed from the buffer tubes using a cutting tool. However, the removal of the binders increases the time required for accessing the cable and may potentially damage the buffer tubes or other cable components.
U.S. Pat. No. 6,088,499 discloses a fiber optic cable which includes a cable core and a sheath section disposed over the cable core. The cable core includes a plurality of buffer tubes housing a plurality of optical fibers, a binder stranded around the cable core, and a ripcord disposed under the binder. The sheath section includes two ripcords, armor tape which surrounds the ripcords, and a jacket which surrounds the armor tape. When it is desired to access the fiber optic cable, the ripcords in the sheath section are pulled to rip the armor tape and the jacket to gain access to the cable core, and then the ripcord in the cable core is pulled to rip the binder to gain access to buffer tubes and the optical fibers therein. However, the additional ripcord in the cable core increases manufacturing costs and is a required step which must be performed in order to access the cable.
In view of the disadvantages of conventional loose tube cables which utilize binders which must be removed in order to access the buffer tubes and optical fibers therein, it is an object of the present invention to provide a solution to the problem of removing binders from fiber optic cables.
The present invention is adapted to achieve the foregoing objects. In accomplishing these objects, a first embodiment of the present invention provides an optical fiber cable comprising a plurality of buffer tubes, binder wrapped around the buffer tubes, a ripcord disposed between the buffer tubes and the binder, and a protective outer jacket covering the buffer tubes. Upon application of a sufficient outwardly directed pulling force, the ripcord rips both the binder and the jacket thereby providing access the buffer tubes and optical fibers therein.
According to a second embodiment of the present invention, there is provide a fiber optic cable comprising a plurality of buffer tubes, binder wrapped around the buffer tubes, a ripcord, and a protective outer jacket covering the buffer tubes, wherein the binder is formed of a material which melts or softens when the jacket is formed by an extrusion process so that the binder is thereby incorporated into the jacket.
According to a third embodiment of the present invention, there is provided a fiber optic cable comprising a plurality of buffer tubes, binder wrapped around the buffer tubes, a ripcord, and a protective outer jacket covering the buffer tubes, wherein the binder is formed of a material which will adhere to the jacket when the jacket is formed by an extrusion process and is easily torn when the jacket is ripped by the ripcord.
According to a fourth embodiment of the present invention, there is provided a fiber optic cable comprising a plurality of buffer tubes, binder wrapped around the buffer tubes, a ripcord, and a protective outer jacket covering the buffer tubes, wherein the binder is formed of a material which will adhere to the jacket and has mechanical properties which will be reduced when the jacket is formed by an extrusion process, and is easily torn when the jacket is ripped by the ripcord.